Belluz: Inequality isn't just unfair — it's making people sick

Inequality has become a popular topic over the past decade. In books like Capital in the Twenty-First Century and Inequality and Instability, economists have warned that the growing income gap is spinning us back to strict 19th-century-style social hierarchies, where elites dominate everybody else, usually on the basis of inherited wealth.

What's usually overlooked in the conversation is how rising inequality can erode our health. This is a subject that Michael Marmot, a British physician and epidemiologist, knows a lot about. He's spent the past 40 years amassing a body of research that shows how inequality can be intrinsically bad for health outcomes — work he's collected in his new book, The Health Gap.

His findings are stunning. Marmot discovered that health and social status are often inextricably linked — even when you control for income, education, and other risk factors. This is true if you look at countries or at cities, or even drill down to the level smaller communities. And the implication of this research is that high levels of inequality can, on their own, make people sick.

Most famously, his Whitehall studies established a link between the relative rank of officers in the British civil service and their risk of disease and death. The higher an officer was ranked, the better his or her health. This was despite the fact that all civil servants were relatively well-off, with similar levels of education. Again, the stratification itself seemed to be the important factor.

Marmot calls the link between health and status "the social gradient in health." One possibility is that it's all related to a sense of control in one's life. People lower down in the social order feel like they have less control, which can lead to stress that then negatively impacts health.

Marmot has documented this social gradient in many other settings around the world. In London, life expectancy drops by one year for every stop heading east on the Jubilee metro line. In Baltimore's inner-city Upton neighborhood, men can expect to live until 63. In nearby Roland Park, an affluent social enclave with safer streets and better job prospects, that life expectancy rises to 83 — an incredible 20-year difference in a tiny geographic area.